Question: at what point during the year do adult gulls start bonding and form a pair?
Literature shows that pairs split up after the breeding season and meet up again during the winter period just before the next breeding season begins. I saw an example of this in February this year when I observed two European Herring Gulls together (ringed as Green F.AAT and Green M.ABB, known to be a pair) although they were not interacting with each other.
Today I still can’t answer the question fully, but I did observe some very interesting behavior that to me came across as pair-bonding.
[Edit: more info has come to light since I wrote this post, see comments at the end of this article.]
Subject is 6th-calendar year Lesser Black-backed Gull (Larus fuscus graellsii) Yellow H.501, ringed in Germany and a regular visitor to my local gull patch.
During my weekly lunch-time break with fellow birder and friend Jan Zorgdrager, we came across H.501 while looking for ringed gulls in my home town of Leiden, The Netherlands. It was part of a group of some 40 gulls which we attracted with bread. Most of the gulls were adult Lesser Black-backed Gulls, plus some adult Herring Gulls as well as juveniles and sub-adults of both species.
During our first encounter of H.501 about a month ago, we already noticed that it had grown up to be a very assertive and vocal individual.
We were therefore not surprised to see it performing the long-call soon after arriving.
Because I’ve recently started to record gull sounds, I was able to record one of his long-calls:
We then noticed some behavior that we have not observed it doing before: it started walking around while performing the mew-call.
At first, it was by itself and it paused at times to tug at some blades of grass (a very light form of grass-pulling).
It then walked a short distance while mew-calling:
We then noticed that it was joined by a second adult, and they both started performing the long-call:
After walking together for a short distance, they were joined by a third adult.
For more than a minute, the 3 of them performed long-calls, contact calls and mew-calls:
H.501 then walked off with one of them, and a whole ritual unfolded, consisting of walking parallel next to each other while mew-calling:
…tugging at the grass:
…sitting on the ground as if positioning on a nest:
…all the while clearly interacting with each other:
…as well as choking in a sitting-down position:
I was able to record the sound that is made during choking as well:
This whole process lasted about 5 minutes and took place just a few meters in front of us. It then repeated itself right up until we left and it possibly continued after that.
Jan Zorgdrager managed to capture part of this fascinating behavior on video:
So what to conclude from this behavior? Is it pair-forming or something else?
Looking at both individuals in the field and while studying the images and video now, I find it hard to sex both gulls. At first I believed that both were males, but after having seen the video I’m tempted to say that H.501 is female and that the un-ringed individual is a male.
If it is not pair-forming than it could be aggressive behavior. Indicators are the wings that are raised from the flanks, the long-calling, mew-calling, grass-pulling and choking, which are all part of antagonistic behavior. Most of this behavior though can also occur between (future) mates.
The whole sequence though doesn’t come across as aggressive to me; there were no charges or raising of the wings as we are known to see in really aggressive encounters. The video clearly shows a tranquil atmosphere of two individuals trying to get to know each other rather than fighting each other. The choking as well did not come across as aggressive but more in line with showing each other a place suitable for nesting.
Niko Tinbergen in The Herring Gull’s World (1960) describes the male’s role in the initial pair forming and how the male gull performs the mew-call, walks with a female to a place nearby to make incomplete nest-building movements. Tinbergen also goes on to say that these movements are indistinguishable from hostile choking.
My knowledge and experience in reading this type of behavior is limited though and at this moment the jury is still out. I will contact some experts to get their take on it.